In the manufacture of photographic films and papers, a support is commonly coated with multiple layers. The different layers have different individual functions in the final product, and in many instances it is necessary that the layers remain distinct and not mix with one another. For example, a simple color photographic film can have a subcoating, a blue-sensitive layer, a green-sensitive layer, a red-sensitive layer, one or more color filtering coatings, etc. Films with about 15 layers have been described, e.g. in EP 257,515.
In forming photographic elements, the layers can be applied to the support by various procedures known in the art. For example, the layers can be applied by dip coating, roller coating, spray coating, bead coating, and the like.
Two or more layers can be simultaneously applied as illustrated by U.S. Pat. Nos. 2,761,791, 3,508,847, 3,539,644, and such other patents cited in Research Disclosure No. 308, December 1989, pp. 1007-8. There, coating and drying procedures are discussed.
It is well known that gelatin is a common matrix for multiple layer products of the type discussed above. Over the past recent decades, simplifications in photographic processing have been made through the use of higher solution temperatures, and the combination or elimination of one or more steps in the process. The application of hardeners to photographic gelatin and advances in hardener technology have made many such improvements possible.
The hardening of gelatin is a crosslinking process. It produces (i) a reduction of swelling in water and aqueous systems, and (ii) an increase in the temperature required for solution in water. Various materials have been suggested for hardening proteinaceous colloids like collagen or gelatin. For references relating to suggested hardeners, reference is made to Research Disclosure, supra, pages 1004-1005.
This invention comprises a modification of gelatin or similar polypeptide that makes it react much faster with a hardener. The modification process involves reaction of some of the --COOH groups attached to the polypeptide(s) with (i) an amide bond forming agent, and (ii) an amine having two or more amino groups. In the method of this invention, only some of the carboxy groups along the peptide chains of the starting colloid are reacted.
The reaction of only a partial number of the --COOH groups with the selected reagents to prepare photographically suitable gelatins is unknown in the art. In U.S. Pat. No. 4,238,480, all of such groups are reacted to prepare a collagen or collagen-like substance with a more electropositive surface, which is used to control or terminate blood loss.
The process of this invention provides materials having unobvious, desirable properties useful in photographic arts and in other technological areas. Accordingly, the processes and the compositions provided by this invention are deemed to be significant advance in the art.